Aminoglycoside Heteroresistance in Acinetobacter baumannii AB5075.
Aminoglycoside Heteroresistance in Acinetobacter baumannii AB5075.
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DOI：
10.1128/msphere.00271-18
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发表时间：
2018-08-15
期刊：
影响因子：
4.8
通讯作者：
Rather PN
中科院分区：
文献类型：
--
作者：
Anderson SE;Sherman EX;Weiss DS;Rather PN
鲍曼不动杆菌已成为世界各地医院的重要病原体，这些感染的发生率一直在增加。由于多药和泛耐药分离株的频率迅速增加，鲍曼不动杆菌感染已变得极其难以治疗。这促使世界卫生组织将鲍曼不动杆菌列为研究和开发新抗生素的首要任务。本研究首次报道了鲍曼不动杆菌氨基糖苷类异源耐药性的详细分析。我们定义了异源耐药的机制基础，其中编码氨基糖苷腺苷转移酶的aadB（ant2″）Ia基因以依赖reca的方式高度扩增。值得注意的是，在没有抗生素选择的情况下，这种20到40个拷贝的扩增在1/200个细胞中随机发生。此外，我们为第二种不依赖reca的氨基糖苷异耐机制提供了证据。本研究揭示鲍曼不动杆菌氨基糖苷耐药性远比以前认识到的复杂，这对使用氨基糖苷类药物治疗鲍曼不动杆菌感染具有重要意义。异耐药是细胞亚群表现出比一般群体更高水平的抗生素耐药性的现象。鲍曼不动杆菌AB5075对妥布霉素的耐药性分析表明，在生长抑制区出现耐药性增加菌落的频率较高。通过种群分析谱（PAP）证实了耐药亚群的存在。妥布霉素耐药亚群对庆大霉素交叉耐药，但对阿米卡星不耐药。增加的妥布霉素抗性表型是高度不稳定的，细胞在非选择性培养基上生长后，以60%至90%的频率恢复到抗性较低的群体。此外，用亚抑制浓度的妥布霉素进行预孵育并没有增加耐药亚种群的频率。在抗生素治疗过程中，妥布霉素耐药亚群显示复制，表明这些不是持久性细胞。在鲍曼不动杆菌AB5075中，一个大质粒（p1AB5075）携带aadB， aadB是一种2″-核苷酸转移酶，使其对托布霉素和庆大霉素都具有耐药性，但对阿米卡星没有耐药性。aadB基因是整合子的一部分，与另外四个抗性基因相邻携带，这些抗性基因的两侧都有一个整合酶基因的拷贝。在耐药性增强的分离株中，该区域以依赖reca的方式高度扩增。然而，在recA突变体中，具有不稳定妥布霉素抗性的菌落是由不涉及该区域扩增的机制产生的。这些数据表明鲍曼不动杆菌中妥布霉素异源耐药至少通过两种机制发生，未来研究确定其对患者预后的影响是有必要的。鲍曼不动杆菌已成为世界各地医院的重要病原体，这些感染的发生率一直在增加。由于多药和泛耐药分离株的频率迅速增加，鲍曼不动杆菌感染已变得极其难以治疗。这促使世界卫生组织将鲍曼不动杆菌列为研究和开发新抗生素的首要任务。本研究首次报道了鲍曼不动杆菌氨基糖苷类异源耐药性的详细分析。我们定义了异源耐药的机制基础，其中编码氨基糖苷腺苷转移酶的aadB（ant2″）Ia基因以依赖reca的方式高度扩增。值得注意的是，在没有抗生素选择的情况下，这种20到40个拷贝的扩增在1/200个细胞中随机发生。此外，我们为第二种不依赖reca的氨基糖苷异耐机制提供了证据。本研究揭示鲍曼不动杆菌氨基糖苷耐药性远比以前认识到的复杂，这对使用氨基糖苷类药物治疗鲍曼不动杆菌感染具有重要意义。
Acinetobacter baumannii has become an important pathogen in hospitals worldwide, where the incidence of these infections has been increasing. A. baumannii infections have become exceedingly difficult to treat due to a rapid increase in the frequency of multidrug- and pan-resistant isolates. This has prompted the World Health Organization to list A. baumannii as the top priority for the research and development of new antibiotics. This study reports for the first time a detailed analysis of aminoglycoside heteroresistance in A. baumannii. We define the mechanistic basis for heteroresistance, where the aadB(ant2″)Ia gene encoding an aminoglycoside adenylyltransferase becomes highly amplified in a RecA-dependent manner. Remarkably, this amplification of 20 to 40 copies occurs stochastically in 1/200 cells in the absence of antibiotic selection. In addition, we provide evidence for a second RecA-independent mechanism for aminoglycoside heteroresistance. This study reveals that aminoglycoside resistance in A. baumannii is far more complex than previously realized and has important implications for the use of aminoglycosides in treating A. baumannii infections. Heteroresistance is a phenomenon where a subpopulation of cells exhibits higher levels of antibiotic resistance than the general population. Analysis of tobramycin resistance in Acinetobacter baumannii AB5075 using Etest strips demonstrated that colonies with increased resistance arose at high frequency within the zone of growth inhibition. The presence of a resistant subpopulation was confirmed by population analysis profiling (PAP). The tobramycin-resistant subpopulation was cross resistant to gentamicin but not amikacin. The increased tobramycin resistance phenotype was highly unstable, and cells reverted to a less resistant population at frequencies of 60 to 90% after growth on nonselective media. Furthermore, the frequency of the resistant subpopulation was not increased by preincubation with subinhibitory concentrations of tobramycin. The tobramycin-resistant subpopulation was shown to replicate during the course of antibiotic treatment, demonstrating that these were not persister cells. In A. baumannii AB5075, a large plasmid (p1AB5075) carries aadB, a 2″-nucleotidyltransferase that confers resistance to both tobramycin and gentamicin but not amikacin. The aadB gene is part of an integron and is carried adjacent to four additional resistance genes that are all flanked by copies of an integrase gene. In isolates with increased resistance, this region was highly amplified in a RecA-dependent manner. However, in a recA mutant, colonies with unstable tobramycin resistance arose by a mechanism that did not involve amplification of this region. These data indicate that tobramycin heteroresistance occurs by at least two mechanisms in A. baumannii, and future studies to determine its effect on patient outcomes are warranted. IMPORTANCE Acinetobacter baumannii has become an important pathogen in hospitals worldwide, where the incidence of these infections has been increasing. A. baumannii infections have become exceedingly difficult to treat due to a rapid increase in the frequency of multidrug- and pan-resistant isolates. This has prompted the World Health Organization to list A. baumannii as the top priority for the research and development of new antibiotics. This study reports for the first time a detailed analysis of aminoglycoside heteroresistance in A. baumannii. We define the mechanistic basis for heteroresistance, where the aadB(ant2″)Ia gene encoding an aminoglycoside adenylyltransferase becomes highly amplified in a RecA-dependent manner. Remarkably, this amplification of 20 to 40 copies occurs stochastically in 1/200 cells in the absence of antibiotic selection. In addition, we provide evidence for a second RecA-independent mechanism for aminoglycoside heteroresistance. This study reveals that aminoglycoside resistance in A. baumannii is far more complex than previously realized and has important implications for the use of aminoglycosides in treating A. baumannii infections.